Fishkeeping in home aquaria is a popular passtime in the US and elsewhere. Most home aquaria have typical water capacities in the range of approximately 10 gallons to approximately 250 gallons, although larger and smaller capacities are available. Living aquatic animals, such as fish, excrete a variety of wastes including ammonia through their gills and urine. Ammonia is toxic to fish at 1 ppm, and a fully established tank should have an ammonia level of approximately 0 parts-per-million (ppm). To maintain a sufficiently low level of ammonia and to remove other particulates virtually all fresh and salt water tanks employ a filtration system. Filters are available in a variety of types and sizes, depending largely upon the capacity of the tank.
One popular type of filter employed in smaller tanks hangs from the rim of the tank, often in the rear, and defines a chamber containing activated charcoal and other filter medium. Water enters the chamber through a siphon tube that extends deep into the tank. Filtered water exits the tank via an open outlet that creates a “waterfall” effect. A sponge is contained in the chamber to support aerobic nitrifying bacteria (nitrosomonas) that digest ammonia and excrete nitrite, which is also toxic, but less so than ammonia. Nitrite is toxic at levels of 5 ppm, and a fully established tank should have 0 ppm nitrite. Other species of aerobic bacteria, nitrosomonas and Nitrospira™ spp., consume nitrite and excrete nitrate. Nitrate is not acutely toxic to freshwater fish (though it is for marine invertebrates). A fully established tank should have nitrate levels below 40 ppm, and marine invertebrate tanks should have readings at approximately 0 ppm. The aforementioned aerobic bacteria grow and consume ammonia and nitrite most actively when they are alternately exposed to air and water. Hence, the most commercially successful filter is Snyder, et. al's Bio-Wheel, sold as Aquaria, Inc.'s Marineland brand. (U.S. Pat. No. 5,423,978 et. seq., which is expressly incorporated herein by reference)
Somewhat larger aquaria may employ a canister-type filter. The canister sits on a stand or in a cabinet remote from the tank and is interconnected to the tank's water supply by an inlet hose and return hose. A pump and/or air supply generates a circulation of water through the filter canister. The canister can included a bacteriological substrate that functions to consume ammonia and nitrite as described above. The canister may also house a particulate filter media, charcoal and/or other components, arranged so as to be accessible by a user for periodic cleaning and servicing. Both rim-mounted and canister-type bacteriological filters are limited by the inability to completely remove nitrogenous compounds from the water. To provide the best conditions for tank inhabitants, frequent water changes that remove these dissolved compounds are highly desirable. However, fresh water is often, itself, incompatible with the tank as it may contain added chlorine (due to municipal treatment) or other compounds that may harm fish.
It is generally accepted in the aquarist's art that photosynthesizing algae (See generally, Adey, Walter and Karen Loveland Dynamic Aquaria: Building Living Ecosystems 2d ed. (Boston: Academic Press 1998); Johnson, Erik and Richard Hess, Fancy Goldfish: A Complete guide to Care and Collecting (New York: Weatherhill 2004)) consume all major kinds of nitrogenous wastes (ammonia, nitrite, and nitrate) and can and should be employed in successful fishkeeping. Algae photosynthesize and thereby produce oxygen, which benefits fish.
Walter Adey describes various algae turf scrubbers in Dynamic Aquaria (1998, 2d. ed., 167-69) and in U.S. Pat. Nos. 4,333,263; 4,966,096; 5,097,795; and 5,851,398, the teachings of which are expressly incorporated herein by reference. Adey's designs generally incorporate a flat substrate upon which algae is cultivated. Adey's substrate is alternately exposed to air and water by various means, including a dump bucket that fills with aquarium water and then dumps onto said substrate, and a system where the substrate is a shallow bucket shaped like a painter's roller-brush tray and mounted on an axis. Adey's substrate bucket sits beneath a light source and tips when it is full, creating an illuminated “wet/dry” surface.
Adey's design for a home algal turf scrubber unit necessitates maintaining a large box over a home aquarium. (See, for example, Adey FIG. 1, U.S. Pat. No. 5,097,795) This design is large, expensive, cumbersome, and hampers an aquarist's access to the water in his or her tank. At the present time Adey's design has not been mass-marketed in the United States—at least not to the extent where it is commonly available in pet stores.
It is desirable to provide a filtration system that employs the highly beneficial photosynthetic and nitrogen-consuming properties of algae, but without requiring a cumbersome and hard-to-service form factor. The filtration system should be applicable to a wide range of tank sizes and occupy a minimal footprint, in keeping with the space limitations and aesthetic dictates of a personal residence.